PSI - Issue 52

Mayu Morita et al. / Procedia Structural Integrity 52 (2024) 195–202 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The remainder of this paper is organized as follows. Next section is devoted to outline the procedures for constructing the composite model and its equilibrium structure using MD simulations. In section 3, we present the simulation results and corresponding discussion. Finally, Section 4 of this manuscript presents the concluding remarks. 2. Simulation Method 2-1. Creating matrix polymer models and composite models The molecular structure of glycol lignin is predetermined by the following experimental facts. (1) The molecular weight is approximately 2000. (2) The ratio of hydroxyl groups (-OH) directly attached to the benzene ring to the hydroxyl groups at the ends of PEG is 1:1. (3) About 75% of the basic structure of lignin is chemically bonded through β -O-4 linkages, ensuring that the glycol lignin has linear structure. (4) There are two or more hydroxyl groups directly attached to the benzene ring per molecule.

Fig. 2 Schematic diagram of interface energy extraction by energy balance calculation Based on these findings, the molecular structures of lignin with and without side chains (PEG) are determined as shown in Figure 1 (a) and (b). The location of the two side chains of PEG is where the potential energy (molecular force-field described below) is the smallest among all combinations of locations. The benzene rings at both ends of these molecules have hydroxyl groups that react with the epoxy groups of DGEBA. Therefore, a pentameric polymer models with alternating polymerization of DGEBA and (glycol) lignin are created for MD simulations. These polymers are denoted by EL and EGL as described in previous section. Pure graphene sheet and three functionalized graphene sheets modified with -OH and -O groups are created. Each functional group is attached to a randomly selected carbon atom on one side of the graphene sheet. The ratio of the number of functional groups to carbon atoms is set to 0.1. All graphene sheets have the same size of 60 Å × 61 Å in area. These molecular models are shown in Figure 1 (c) - (e). For the interface models constituting of polymer and reinforcement, a three-layer graphene model is first created. In this layer structure, functionalized graphene is placed in the first and third layers with the functional groups on the outside, and pure graphene is placed in the middle layer. Multiple polymers of EL or EGL are randomly arranged above and below the graphene layer to create a polymer/graphene/polymer sandwich structure, which is regarded as an interface model. In our simulations, the Particle Mesh Ewald (PME) method is used to calculate the Coulombic interactions using the Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA) force field for reproducing detailed molecular